Could water lettuce — considered an invasive, exotic plant by the Florida Fish and Wildlife Conservation Service and often controlled with chemical herbicides — be harvested for beneficial purposes?
While FWC considers this plant an invasive species, it has been in Florida a long time. According to FWC’s invasive plants website, “This floating plant native to South America is considered to be one of the worst weeds in the subtropical and tropical regions of the world. In Florida, it was first recorded in 1765; its introduction is linked to early shipping commerce between Florida and South America.”
While manatees eat water lettuce, it can be detrimental to other wildlife, according to FWC. The website notes: “Water-lettuce populations often form large expanses of dense, impenetrable floating mats limiting boat traffic, recreation, flood control and wildlife use. These dense canopies at the water surface shade out native submersed plant species and can uproot native emergent plants that are important to wildlife.”
“Effects of allelochemical extracted from water lettuce (Pistia stratiotes Linn.) on the growth, microcystin production and release of Microcystis aeruginosa,” by Xiang Wu, Hao Wu, Junren Chen and Jinyun Ye was publised in Environmental Science and Pollution Research in 2013.
The researchers looked at a chemical found in water lettuce and the effects of that chemical on the Microcystin aeruginosa. “This study explored the optimization of a method of extracting allelochemicals from Pistia stratiotes Linn., identified the optimal dose range for the allelochemicals’ anti-algal effect and investigated their impact on the growth of Microcystis aeruginosa, as well as the production and release of microcystin,” the authors explained. They measured changes in algal cell density and chlorophyll A content.
They found “the application of allelochemicals from P. stratiotes to inhibit M. aeruginosa has a high degree of ecological safety and can be adopted in practical applications for treating water subjected to algae blooms because the treatment can effectively inhibit the proliferation of algal cells without increasing the release of cyanotoxin.” An allelochemical is a chemical produced by a living organism, exerting a detrimental physiological effect on another species when released into the environment.
In recent years, Microcystis aeruginosa have been the dominant cyanobacteria in many algal blooms on Lake Okeechobee. Microcystis aeruginosa does not always produce toxins, but it is capable or producing toxins. It has been documented in some cases to produce toxins in Lake Okeechobee as well at the St. Lucie canal and the St. Lucie River and the Caloosahatchee River.
Another study, “Allelopathic Effects of Pistia stratiotes (Araceae) and Lyngbya wollei Farlow ex Gomont (Oscillariaceae) on Seed Germination and Root Growth” by Jehangir H. Bhadha, Timothy A. Lang, Odiney M. Alvarez, Mihai C. Giurcanu, Jodie V. Johnson, Dennis C. Odero, Samira H. Daroub, was published by the Canadian Center of Science and Education in 2014.
First, some help with the title of that report.
• Allelopathy is a biological phenomenon where one plant inhibits the growth of another.
The authors note “Pistia stratiotes and Lyngbya wollei are the two most common aquatic weeds that flourish in farm canals within the Everglades Agricultural Area of Florida. Identifying a useful application of these weeds would not only address important environmental concerns, but would also be an incentive for farmers to harvest it. The objective of this study was to determine use of P. stratiotes and L. wollei as soil amendments for stimulation of seed germination and root growth in different plant species.”
The researchers studied the effects of dried and ground water lettuce and L. wollei on germination and root length of snap bean, corn, sorghum, common lambsquarters, and rice, using a controlled petri-dish incubation bioassay study. Overall, both amendments had a negative allelopathic effect on germination of most vegetables plants, but there was a significant positive increase in rice root length in response to P. stratiotes rate over the two-week period. This study showed that water lettuce can be used as a potential bio-fertilizer to stimulate early growth of rice.